High voltage silicon carbide (SiC) devices can handle voltages above about 600V or more. Such devices may handle as much as about 100 amps or more of current, depending on their active area. High voltage SiC devices have a number of important applications, particularly in the field of power conditioning, distribution and control. High voltage semiconductor devices, such as Schottky diodes, MOSFETs, GTOs, IGBTs, BJTs, etc., have been fabricated using silicon carbide.
Schottky barrier diodes are used extensively as output rectifiers in switching-mode power supplies and in other high-speed power switching applications, such as motor controls, for carrying large forward currents and supporting large reverse blocking voltages. Diodes exhibit low resistance to current flow in a forward direction and a very high resistance to current flow in a reverse direction. A Schottky barrier diode produces rectification as a result of nonlinear unipolar current transport across a metal semiconductor contact.
Silicon carbide (SiC) Schottky diodes are a promising technology because such devices can provide a low forward voltage drop, high breakdown voltage, and fast switching speed with essentially no reverse recovery current. However, the operational characteristics of a Schottky diode can depend heavily on the type of metal used for the Schottky contact. The power dissipated by a Schottky diode depends on the forward voltage drop and the reverse leakage current, both of which should be as low as possible. The forward voltage drop and the reverse leakage current are related to the barrier height of the Schottky contact, i.e., the magnitude of the potential barrier between the metal and semiconductor regions of the Schottky contact.
A low barrier height metal will have a low forward voltage drop and a large reverse leakage current. Conversely, a high barrier height metal will have a larger forward voltage drop and a smaller reverse leakage current. Therefore, it is desirable to have a Schottky diode which exhibits the forward characteristics of a small barrier height metal and the reverse characteristics of a large barrier height metal. A trench type Schottky diode can be configured to partially satisfy these conflicting design criteria by using lines of high barrier metals to pinch-off or electrically shield intervening trenched lines of low barrier metals. Although such trench type Schottky diodes may provide improved forward and reverse operational characteristics, their fabrication cost may be increased by the processes needed to form the trenches and high/low barrier metal lines, and their forward and reverse characteristics can be limited by the trench and high/low metal line feature sizes that are obtainable.
SiC PIN diodes are very attractive for RF limiter applications. In particular, the high breakdown strength and high thermal conductivity of SiC may enable much higher RF power levels and faster switching speeds than may have been possible using silicon (Si) or gallium arsenide (GaAs) technologies. In these applications, a Schottky diode is commonly used to rectify the RF signal and produce a bias current for the PIN diode, which will limit the RF signal to acceptable levels. The barrier height of the Schottky diode used in these applications should be relatively low to rectify low-level RF signals. Many applications require a barrier height of 0.5 eV or less. However, most commonly used materials, such as chromium (Cr) and Titanium (Ti) only provide barrier heights of about 0.8 eV or higher on SiC.